During catalytic processes wherein hydrocarbon feedstocks are treated with hydrogen, carbonaceous matter and metals such as vanadium and nickel are usually deposited on the catalysts, which causes a gradual decline of catalytic activities. When catalyst particles have become deactivated to an unacceptable degree they have to be replaced by fresh and/or regenerated catalyst particles.
Conventionally, catalyst particles which gradually have become deactivated are replaced in a procedure which requires terminating the conversion process by allowing the temperature and pressure to decrease substantially (e.g. by means of a quench liquid) before unloading deactivated catalyst particles and loading fresh and/or regenerated catalyst particles.
Catalyst unloading processes are disclosed for instance in U.S. Pat. No. 3,883,312 wherein a substantially vertically cylindrical reactor is described having separate inlet means for reactant and catalyst at the upper part of the reactor, and containing catalyst bed supporting and guiding means comprising one or more screen sections for withdrawal of reactor effluent from the catalyst, the reactor being further provided with separate outlet means for reactor effluent and catalyst in a lower part of the reactor. Fresh and/or regenerated catalyst particles can be introduced continuously or periodically to such reactors and spent catalyst particles can be withdrawn continuously or periodically from such reactors.
It should be noted, however, that during the first mentioned conventional unloading procedure substantial temperature and pressure variations occur which may cause undesirable stress problems with respect to the reactor vessel, valves and solid materials concerned. Moreover, during unloading undesired reactions may occur which adversely affect product quality since the feed may be in contact with spent catalyst particles over too great a period of time. Furthermore, a substantial amount of time will be required to carry out such unloading operations.
In view of above it would be of importance to investigate whether it would be possible to transport oil inside the reactor under substantially operating conditions without contacting catalytic material during said transport, in particular during unloading procedures.